State-of-the-art circuit breakers and circuit interrupters such as described within U.S. Pat. No. 4,672,501 entitled "Circuit Breaker and Protective Relay Unit" employ digital circuitry to perform overcurrent protection along with supplementary protection function. The so-called "electronic trip units" within such circuit breakers have here-to-fore been limited to industrial applications in view of the added costs associated with the electronic trip unit components. To provide electronic input to the circuit interrupters from associated electrical equipment, transducers such as current transformers described in U.S. Pat. No. 4,591,942 entitled "Current Sensing Transformer Assembly", Hall effect devices, such as described in U.S. Pat. No. 5,615,075 entitled "AC/DC Current Sensor for a Circuit Breaker" and GMR (Giant MagnetoResistor) devices as described in U.S. patent appliation Ser. No. 09/006,794 entitled "Circuit Interrupter Having Improved Current Sensing Apparatus" are often required.
Typically, the current transformers usually provide two functions within the electronic trip unit circuit. The first function is to provide operating power to the electronics within the trip unit and the second function is to provide electronic signals representative of the magnitude of the current flowing within each phase of a multi-phase electrical distribution system. U.S. Pat. No. 5,583,732 entitled "Modular Current Transformer for Electronic Circuit Interrupters" describes a recent approach to combine the two functions within a single modular arrangement at a savings in both material costs and manufacturing assembly costs. A separate current transformer is required within each phase of a multi-phase electrical circuit.
When overcurrent protection is provided in residential applications, circuit breakers employing thermal magnetic trip units are installed within the residential load centers for protecting the main and branch circuits connecting with the load centers. U.S. Pat. No. 4,513,268 entitled "Automated Q-Line Circuit Breaker" describes one such residential circuit breaker including a thermal magnetic trip unit for overcurrent protection.
U.S. Pat. No. 4,667,269 entitled "Circuit Breaker Support Saddle Having A Split Neutral Connector" and U.S. Pat. No. 4,646,198 entitled "Molded Case Circuit Breaker Modular Support Assembly" disclose compartments arranged for housing a main circuit breaker along with a plurality of branch circuit breakers electrically connected in series with the main circuit breaker.
When such thermal magnetic circuit breakers are employed in such residential load centers, the use is limited to overcurrent circuit protection. Ground fault and arcing fault function must be added to the circuit breakers by means of ground fault and arcing fault modules that are attached to the circuit breaker enclosure at further cost increase. On such arcing fault module is described within U.S. patent appliation Ser. No. 09/006,796 entitled "Arcing Fault Detection Module".
Accordingly, attempts to incorporate a so-called "smart" circuit breaker having an electronic trip unit in a residential load center for providing additional protective features to the load center have not proven economically feasible to date. The need of a current transformer to provide both operating power and sensing function to the electronic trip unit increases both the size of the circuit breaker as well as the overall cost since the current transformers are usually contained within the circuit breaker enclosure, along with the circuit breaker operating mechanism, contacts and trip unit.
It would be beneficial to provide a separate circuit for providing operating power to the trip unit in combination with small-sized electronic transducers for determining the current magnitude in view of cost and size restraints with 2-pole circuit breakers used within residential load centers. A further benefit is the use of an option plug in the form of a removable electronic circuit to enable the trip unit to perform ground fault, arcing fault and their combination.
One purpose of the invention accordingly, is to describe an inexpensive smart circuit breaker having an electronic trip unit with an electronic transducer within each pole of a 2-pole circuit breaker and an equivalent circuit within at least one of the poles to supply operating power to the trip unit.